This invention relates to aeration apparatus and more particularly to an improved apparatus for the production of small gas bubbles in a liquid in order to create a large interfacial area between the gas and the liquid, thereby increasing the efficiency of processes such as flotation and gas liquid mass transfer.
Although the apparatus may be of value in other fields such as aeration and gas absorption, the invention will be described in relation to the flotation process.
The art of flotation generally involves the aeration and agitation of a slurry or suspension in water of finely divided ore particles in a cell or apparatus of suitable design. The mineral may be regarded as a mixture of valuable minerals or "values", and clay, rock or other unwanted "gangue" particles. The object of the process is to remove the values from the gangue, and this may be achieved by conditioning the slurry with chemical reagents which have the effect of rendering the values selectively hydrophobic or water repellent, while leaving the gangue particles hydrophilic or wettable. Thus when a hydrophobic particle comes into contact with a bubble, it will attach and rise with it to the surface of the liquid where it forms a froth which may be scraped off into a launder, thereby conveying the values out of the cell and separating them from the gangue, which remains with the liquid in the cell. To assist in the formation of a stable froth, it may be necessary to add chemical frothing agents.
Flotation machines as customarily constructed consist of a tank in the base of which is an aerating rotor and a concentric stator. Air is introduced into the vicinity of the rotor which rotates on a suitably placed shaft, and is broken up into small bubbles by the action of blades or fingers mounted on the rotor, which is frequently of a disc formation. The rotor provides the additional function of keeping the mineral particles in suspension.
Since the valuable mineral is removed from the cell at the surface of the gas bubbles, it is evident that the rate of removal of the particles will depend on the total gas-liquid interfacial area produced in the cell. Thus for a given rate of introduction of air, the smaller the gas bubbles produced by the rotor, the greater will be the interfacial area and hence the more efficient will be the removal process.
The need for more efficient flotation of mineral particles, especially of fine particles smaller than ten microns in diameter, has become more evident in recent times with the depletion of easily worked mineral deposits around the world. It is increasingly found that when new deposits are exploited, the ores are complex and require fine grinding to release the individual mineral particles. Further, in existing mineral concentrators there is a need to improve the recovery of fine particles which hitherto had been allowed to go to tailings, in order to improve the economic performance of the mine.
It is therefore desirable to provide a flotation mechanism which can divide large quantities of gas into very small bubbles to achieve high metallurgical efficiency, while at the same time providing sufficient agitation to maintain the solids in suspension and yet produce a relatively calm surface between the froth layer and the slurry in the flotation cell.
The mechanism should also satisfy practical requirements such as simplicity of construction and operation, long life, easy maintenance and repair, and should be able to be made of wear-resistant and corrosion-resistant materials.